Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$43.46	12.265%	$48.7904	$48.79	$48.80	$48.80
Purchase #2	$250.31	5.473%	$264.0095	$264.01	$264.00	$264.00
Purchase #3	$5.53	11.310%	$6.1554	$6.16	$6.15	$6.20
Purchase #4	$66.59	13.511%	$75.587	$75.59	$75.60	$75.60
Purchase #5	$94.41	6.789%	$100.8195	$100.82	$100.80	$100.80
Purchase #6	$104.32	11.162%	$115.9642	$115.96	$115.95	$116.00
Purchase #7	$53.91	3.712%	$55.9111	$55.91	$55.90	$55.90
7 purchase totals =	$618.53		$667.2371	$667.24	$667.20	$667.30